You can use cd.. to come back to Cdrive in command prompt and "cd new" to open the "new" file. Here "new" is the file in which the image and compressed song are kept. After opening the new file location in the command prompt type the following:
copy / b image.jpg+song.rar image.jpg
You will then see it has been copied and the size of the image in the file has increased
To extract the files, right click on the image and click add to archive. Then click ok.
And that's it! This is how you can retrieve the song hidden in the image file.